Hydrogenation of amides over copper chromite is known in the art. In an article by Wojcik, B. and Adkins, H. in J. Am. Chem. Soc. 1934, 56, 2419-24 there is a general discussion of hydrogenation of amides over copper chromite. The authors of this work came to the conclusion that a diluent such as dioxane was necessary for the by-product water in order to make this process function satisfactorily.
In Pat. No. 3,190,922 (1965) to LeBard, N. M. et al., there is disclosed a process for hydrogenation of N,N-dialkyl amides at low pressures over copper chromite. In this process the water which is produced is continually removed. As pointed out Col. 1, lines 30-36, typically this reaction is carried out at a pressure greater than 200 atmospheres with dioxane as the solvent. This work does not appear to contemplate hydrogenation of lactams.
Deterrents to those in the art desiring to commercialize such a process include the high pressure, handling and removing the solvent, inability to recycle and the number of side reactions which limit the yield and purity.
U.S. Pat. No. 3,444,204 to Schutt et al. discloses a process for the continuous production of higher alkyl-tertiary amines over a copper chromite catalyst in the presence of solvents using at least a 50-fold excess of hydrogen. In this reference the flow rate of amides was 0.07 to 0.33/ml/ml cat./h. The use of lactams was not taught or suggested in this reference.
King discloses in U.S. Pat. No. 4,448,998 a process for producing tertiary amines containing from about 10 to about 72 carbon atoms by hydrogenation of the corresponding N,N-disubstituted amides over a copper chromite-zeolite catalyst. Improvements in conversion and selectivity are attributed to the zeolite. Again, the use of lactams was not contemplated.
In German Pat. No. 28 13 162, Schroeder, W. and Mercker, H. J. teach the continuous hydrogenation of N-methylpyrrolidone over copper on alumina at a flow rate of 0.11-0.33 ml/ml cat./h. The German reference suggests that the use of pressure over 3500 psig is necessary for this type of reaction. The pressure used, as reported in the examples, is about 3626 psi. It is noted that the conversion is high, but overall productivity is relatively low. Removal of by-product water is apparently accomplished by using caustic.
It would be an advance in the art if a process for the hydrogenation of N-methylpyrrolidone could be accomplished under milder conditions and, in addition, exhibit improved productivity. It would be especially desirable if such a process would lend itself to recycling and continuous conversion.
The instant invention provides a method for producing pyrrolidines from pyrrolidones. In particular high selectivities to N-methylpyrrolidine are observed using lower pressure and moderate temperature. Higher space velocities result in higher yield per catalyst volume compared with the closest art. An additional feature is that the pyrrolidine product can be isolated by extraction of the product mixture by specified hydrocarbons followed by distillation, and the hydrocarbon used as the extraction solvent can be recycled. As mentioned, the art suggests removal of water from the product by using a caustic.